Production of plastics derived from renewable resources is expected to grow to 3.45 million tons by the year 2020 which represents a current annual growth rate of approximately 37% for biobased plastics (Plastics Engineering, February 2010, p16-19). The drivers for growth of biobased plastics include the contribution to global warming from production of petroleum-based plastics, the need to reduce our dependence on limited supplies of petroleum oil, the fluctuating petroleum oil prices as well as environmental disposal problems of common petroleum-based plastics. The objective for manufacturing biobased plastics is to replace as much “fossil” or petroleum-derived carbon with “renewable” carbon in the material as possible. The percentage of “renewable” carbon can be qualitatively measured in polymer materials using 14C radio carbon dating (ASTM D6866 test method).
Examples of biobased polymers produced from renewable resources include polyethylene (PE) produced from sugarcane ethanol (Braskem's Green Polyethylene), polylactic acid (PLA) made from corn sugar (Nature Works Ingeo™ PLA), polyhydroxyalkanoates (PHA's) produced by the fermentation of glucose (U.S. Pat. Nos. 6,593,116 and 6,913,911 as well as US Patent Pub. No. 2010/0168481) and thermoplastic starch derived from plants such as potato, corn and tapioca. Reportedly, the most commercially important bioplastics by the year 2020 will include starch-based polymers, PLA, PE, PHA and epoxy resins (Shen et al., (2010), Biofuels, Bioproducts and Biorefining, vol. 4, Iss. 1, p25-49).
Polyhydroxyalkanoates are unique materials to use as components in biodegradable plastic blends because they are easily blended with many other plastics, they can be manufactured as 100% biobased materials, their compositions can be varied to provide very rigid to very flexible substrates and they biodegradable in a number of different environments (water, soil, compost). Blends of PHA's with other biodegradable plastics have been investigated previously such as blends of PBS and PBSA with P3HB-co-4HB (International Pub. WO2010/151798); blends of P3HB-co-4HB with polybutylene-adipate-terephthalate (PBAT) (US Pub. No 2011/0189414) and blends of P3HB-co-4HB with polyvinyl acetate (PVAc) (International Pub. No 2011/031558). While the above blends showed improved mechanical properties and a range of biodegradation rates, the blends did not have properties that enabled them to be used for blown film applications which require high toughness, tear resistance and puncture resistance.
Therefore, a need exists for producing biodegradable plastic blends with improved toughness, tear and puncture resistance properties.